#include <stdio.h>

int Sum(int a)
{
    int sum = 0;
    int i = 1;
    for(i = 1; i <= a; i++)
    {
        sum += i;
    }
    return sum;
}

int main()
{
    int a = 100;
    scanf("%d", &a);
    int ret = Sum(a);
    printf("%d\n", ret);
    return 0;
}
